Ok, I've got another childhood movie that I can't seem find on the net anywhere.

I don't remember much at all about the plot. I remember there were some sort of large hostile aliens, that (I think) preferred being in tunnels or underground. The biggest hint I can think of was the aliens had some type of energy weapon built into their arm, and it was fueled by copper... I believe. I just remember there was a kid at one point that discovered you could load the alien weapons with a penny. I seem to recall the aliens using long "bricks" of copper usually to fuel the weapons.

Also there was some kind of helpful alien that looked sorta like a ninja. In all black. Don't remember if he had weapons or anything... at least I think he was in this movie, hope I'm not confusing it with something else.

I was totally off with the ninja-looking alien. Any clue where he may have been from? I seem to recall him having glowing eyes, all black, and at some point he gets wounded in the movie. I think he was part of an alien group, but all of his aliens friends had different looks. They were friendly with people, and if I remember right, they were helping humans with an evil alien race. I'm pretty sure this was a late 80's / early 90's movie. Least that's when I saw it.

Yup, took place on Earth. The time frame was period (seem to remember black/white police cars, regular clothing on the humans). Think there was a scene when the ninja-alien (I don't recall him actually using martial arts or anything, he just kinda looked like one) being injured and brought into a house. And I don't think he was wearing clothing to give the ninja image, kinda looked like it was his regular skin. Could be wrong.

Your movie about the alien "ninja" could be I Come in Peace. It's about two aliens, both really tall. One is blonde and harvesting dope from people's brains. The other is dark haired and is a cop tracking the dope dealer down. He gets injured, tells the human good guys what's going on, and gives them a weapon. His eyes didn't glow, but they were very bright white with yellow (or light blue) irises, could have been mistaken for glowing compared to his dark hair and costume.